Focus on Cellulose ethers

Why does the volume of mortar increase after adding cellulose ether?

1. Introduction to cellulose ether:

Chemical Structure: Cellulose ethers are water-soluble polymers derived from cellulose, a natural polysaccharide found in plant cell walls. It consists of repeating glucose units linked by β-1,4-glycosidic bonds.

Hydrophilicity: Cellulose ether is hydrophilic, which means it has a strong affinity for water.

2. The role of cellulose ether in mortar:

Water retention: One of the main functions of cellulose ether in mortar is to enhance water retention. It forms a thin film around the cement particles, reducing water evaporation and ensuring a longer hydration process.

Improve workability: Cellulose ether acts as a rheology modifier to improve the workability of mortar. This is especially important for applications such as plastering and rendering.

3. Effect on mortar volume:

Water Absorption: The hydrophilic nature of cellulose ethers enables them to absorb water from the mixture. As it expands, the total water content in the mortar increases, causing volume expansion.

Air Entrainment: Adding cellulose ethers may introduce air into the mortar. Trapped air bubbles contribute to volume gain.

Pore structure: Cellulose ethers can affect the microstructure of the mortar, forming a more porous network. This change in pore structure results in a significant increase in volume.

4.Hydration process and volume expansion:

Delayed hydration: Cellulose ethers can slow down the hydration process of cement. This delayed hydration allows for a more even distribution of water within the mortar, which may result in an increase in volume.

Curing effect: The extended water retention promoted by cellulose ethers helps extend the curing time, allowing the cement particles to more completely hydrate and affecting the final volume of the mortar.

5. Interactions with other ingredients:

Binder interaction: Cellulose ethers interact with cement binders to form a stable matrix. This interaction affects the alignment of the particles and leads to volume expansion.

Admixture synergy: If cellulose ethers are used together with other admixtures, a synergistic effect may occur, affecting the total volume of the mortar.

6. Particle dispersion and distribution:

Uniform dispersion: When cellulose ether is properly dispersed in the mortar, it can make the particle distribution more uniform. This uniformity affects the packing density and thus the volume of the mortar.

7. Environmental conditions:

Temperature and Humidity: Environmental conditions such as temperature and humidity can affect the behavior of cellulose ethers in mortar. Swelling and water absorption properties may vary under different environmental conditions, affecting volume.

8. Conclusion:

In summary, the volume increase observed upon addition of cellulose ethers to mortars is the result of complex interactions including water uptake, delayed hydration, air entrainment, and changes in the mortar microstructure. Understanding these mechanisms is crucial to optimize the use of cellulose ethers in mortar mixtures and achieve the desired properties in construction applications.

Post time: Dec-01-2023
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